B-cell antibodies, Ia-like determinants, and their relation to MLC determinants in man.

The HLA supergene is located in the 6th chromosome. Its position to the centromere and the position of a number of polymorphic isoenzymes has been elucidated. The HLA supergene codes not only for determinants present on all nucleated cells, but also for determinants present on B cells and absent from T cells and platelets. These determinants can be recognized by serology, and evidence is presented that some of them are coded for by a hither to unrecognized locus Ag, which is very closely linked to the MLC determinants of the D locus can be recognized with the help of the MLC test using unprimed cells, homozygous for the MLC determinants, so-called typing cells primed against one MLC determinant in the PLT test. So far, 8 MLC determinants have been recognized. Significant disease-association studies in different racial groups appear to be especially informative. They already indicate that the association found so far must rest on different mechanisms. Whether some of them could be caused by partial deficiency for one or more of the complement factors remains to be proven.